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Fixed bug 2139 - SDL_CreateWindow/WIN_GL_LoadLibrary fails due to external iconv not being able to convert path 

J?nis R?cis

Brief history:

We recently ported a game from SDL 1.2 to SDL 2. While doing Windows testing, I soon discovered that the game exits without opening a window with my cross-compiled SDL2.dll, but works great with the SDL2.dll from the MinGW SDK on libsdl.org. It was as simple as swapping out the DLLs to make it work.

Running the game in Wine showed that the game actually does run, up until the call to SDL_CreateWindow, which fails and leads the game to print out an error:

Failure to create window (LoadLibrary("OPENGL32.DLL"): (null))

Which basically says that there was no error, but maybe that's a Wine quirk.

The error string originates in SDL_windowsopengl.c, in WIN_GL_LoadLibrary, which contains this piece of code:

    wpath = WIN_UTF8ToString(path);
    _this->gl_config.dll_handle = LoadLibrary(wpath);
    SDL_free(wpath);
    if (!_this->gl_config.dll_handle) {
        char message[1024];
        SDL_snprintf(message, SDL_arraysize(message), "LoadLibrary(\"%s\")",
                     path);
        return WIN_SetError(message);
    }

After some digging, I discovered the culprit: WIN_UTF8ToString returns NULL. Why? Because it calls iconv_open from an iconv.dll that does not support the UCS-2-INTERNAL encoding. Why does the official SDL2.dll work? Because it calls no external iconv functions at all.

It turns out that the Fedora MinGW infrastructure (from which I obtained the conventiently prebuilt iconv.dll) does not provide a DLL from libiconv, but instead provides a DLL from a minimal Windows library called win-iconv. Which knows a good bit, but doesn't know anything about UCS-2-INTERNAL:

http://code.google.com/p/win-iconv/source/browse/trunk/win_iconv.c#155

So there are two problems here:

1) The error message is clearly useless, because LoadLibrary is an innocent bystander. Instead wpath should probably checked for NULL, and a more appropriate error should be set. Ideally something that makes it clear than an external iconv is causing trouble.
2) SDL doomed itself at the ./configure step, by finding an existing iconv and happily using it without confirming support for the mandatory encodings required by SDL.

There are certainly a few easy ways out of the situation (although I didn't yet manage to figure out how to prevent ./configure from looking for external iconv), but this had me completely stomped for a good while, so I figured it's worth writing down if anything.

(Search also found this, which talks a little about using UTF-16LE instead of UCS-2-INTERNAL: https://bugzilla.libsdl.org/show_bug.cgi?id=2075)
This commit is contained in:
Sam Lantinga 2013-10-18 00:13:51 -07:00
parent 7ae171d15e
commit a329c7f1c9
1 changed files with 2 additions and 4 deletions
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6
src/core/windows/SDL_windows.h
View File

@ -35,11 +35,9 @@
#include <windows.h>
/* Routines to convert from UTF8 to native Windows text */
/* !!! FIXME: should we force Unicode at this point? */
#if UNICODE
/* !!! FIXME: UCS-2 should be UTF-16 on Windows. */
#define WIN_StringToUTF8(S) SDL_iconv_string("UTF-8", "UCS-2-INTERNAL", (char *)(S), (SDL_wcslen(S)+1)*sizeof(WCHAR))
#define WIN_UTF8ToString(S) (WCHAR *)SDL_iconv_string("UCS-2-INTERNAL", "UTF-8", (char *)(S), SDL_strlen(S)+1)
#define WIN_StringToUTF8(S) SDL_iconv_string("UTF-8", "UTF-16LE", (char *)(S), (SDL_wcslen(S)+1)*sizeof(WCHAR))
#define WIN_UTF8ToString(S) (WCHAR *)SDL_iconv_string("UTF-16LE", "UTF-8", (char *)(S), SDL_strlen(S)+1)
#else
/* !!! FIXME: UTF8ToString() can just be a SDL_strdup() here. */
#define WIN_StringToUTF8(S) SDL_iconv_string("UTF-8", "ASCII", (char *)(S), (SDL_strlen(S)+1))